I've always been puzzled by the cliam that lack of dinosaur bones at the K-T boundary is evidence against their extinction by the impact event. On first impulse, it seems that dino bones should be found in sediments right up to, and on the boundary, but a little thought on the mechanics of fossilization suggests something quite different.
In one of his books Robert Bakker dismissed the impact as the cause of the great extinction and asked, ". . .where are the piles of dinosaur bones? ." But we have only to look at a recent near-catastrophic event for the answer. During the late 1800s the High Plains of the Western US saw the wholesale slaughter of millions of bison, most left on the ground after being stripped of their hides, yet now there is scarcely a trace left of those animals. Of course the flesh rotted quickly, but the bones too begin to disintegrate rapidly under the great temperature swings and oxydizing conditions and destructive organic influences at the surface. Who hasn't seen a splintered fragment of bone in the prairie or the desert, a last testament of life so obviously soon to disappear altogether.
The simple truth we learned in our first geology class, and which still holds, is that rapid burial is essential to the preservation of organic remains. This is especially true for land environments where erosion, rather than deposition, dominates over most of the surface and highly mobile, efficient scavengers constantly scour the land to clean up organic remains. The only common terrestrial environments where animals are likely to be buried and preserved are located in the low ground around waterways, sites for occasional drownings and quick burial on flood plains and in channels.
I've heard that the iconic T-rex had an extraordinarly well developed sense of smell, based on an anlysis of the skull. This would have been useful in locating prey animals but undoubtedly would have been to great advantage in finding dead and decaying ones as well. I doubt that the mighty rex would have had any qualms about it. How deeply would he dig to uncover a carcass buried by a flash flood? The highest dinosaur bones I've heard of occur about 4 feet below the K-T boundary, which sounds like a reasonable depth to protect a burial from scavengers. Is it unreasonable to expect that anything more shallow would have been susceptible to being disinterred? Dogs have been trained to detect human burials at this depth, even deeper, and I suspect that the dinosaurs were at least as capable in this area.
To be honest, I would have been surprised to hear that dinosaur bones were common right up to the level of K-T. It would have meant that they weren't doing the job that nature designed them for
If I may address this issue -There are multiple reasons for there being no fossils right at the boundary.1) Dinosaurs were never extremely abundant in the first place.2) Only an extremely small percentage of the fauna alive at a certain point in time is preserved in the fossil record. They pretty much have to be buried immediately in fluvial or marine sediments - a very rare occurrence.3) It seems likely that the impact that cause the extinction event also caused an acid rain of global proportions and great intensity. I have not seen any speculation on its effect on carcasses and skeletons - perhaps it contributed to destruction of any bones that were left from the dying off.4) Only a very small percentage of the K/T boundary is currently exposed. No bones have been found in the boundary layer YET.These 4 points are what occur to me off the top of my head. There may be others.In support of point 3 - I have collected reworked Cretaceous fossils (ammonites) just above the boundary that seemed to be considerably etched. This may have been purely mechanical rather than chemical, I admit.Pardon my ignorance, I keep read that there hasn't been any dinosaur fossils found in the impact layer, fossils have only been found below the iridium layer, but nothing in it and that it is an extremely small layer. If it caused the dinosaur extinction why no fossils?Bre-- Check out http://groups.yahoo.com/group/californiadisasters/ Read my blog at http://eclecticarcania.blogspot.com/ My Facebook: http://www.facebook.com/derkimster Linkedin profile: http://www.linkedin.com/pub/kim-noyes/9/3a1/2b8 Follow me on Twitter @DisasterKim
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